In some applications, axial needle roller bearings are provided with races having a convex rolling element contact surface in cross section, such as shown in U.S. Pat. No. 5,975,763. This design allows the races to deform with increasing load so that the contact between the needle rollers and the races is proportional to the applied load, allowing the load bearing capacity of the bearing to proportionately increase under an applied load. This arrangement is indicated as increasing bearing life and is said to reduce noise and optimize efficiency under variable load conditions. However, it has been found that this arrangement can be noisy under light loads. Further, the profiled raceways create high contact pressures due to the reduced contact area, which results in poor formation of the lubrication film.
In certain applications, such as torque converter axial bearings, the load is not applied at a constant radial position due to expansion of the torque converter, resulting in the axial load contact position shifting radially outwardly on the bearing ring, which places a higher axial load on radially outer regions of the needle rollers which can, in effect, pinch the rollers at their outer ends. This also can result in higher noise, due to the races contacting the chamfered or rounded end edges of the rollers which are not entirely uniform, depending on the manufacturing process. Using flat washers as the raceways also does not necessarily reduce edge loading in these conditions.
It would therefore be desirable to provide an axial needle roller bearing with which is an improvement over the drawbacks of the known prior art.